Influence of major inherited faults zones on gravitational slope deformation: A two-dimensional physical modelling of the La Clapière area (Southern French Alps)

Abstract

Inherited faults are known to influence rock slope stability and gravitational deformation. In spite of that, in many studies few faults are identified in field and properly used in models of gravitational slope deformation. The aim of this work is to study the influence of inherited faults zone density and geometry on gravitational failure processes at the massif scale using a physical modelling technique which satisfies the similarity criteria. Models are scaled to the well-documented natural example of La Clapière in the Southern French Alps. Experiments were conducted using mechanically homogeneous material with variable fault geometry. In each of tested configurations, the mobilized volume was almost the same. Results confirmed the hypothesis that the La Clapière landslide is a shallow section of a deep-seated gravitational slope deformation. Furthermore, among the various configurations tested, only one is enable to reproduce the observed superficial deformation on the La Clapière hillside. This result demonstrated that the geometry of the faults at depth plays a major role on the style of gravitational deformation patterns. Regarding the particular case of La Clapière, our results give new insights on the shape of the faults affecting the massif at depth. In particular, normal listric faults seem to have shallow inflexions compared to a deep-seated thrust fault that was either gravitationally formed or pre-existing but inactive (i.e. sealed) before slope destabilization and then gravitationally reactivated.